1. Field of the Invention
The present invention pertains to devices for controlling the flow of fluid. In particular, it pertains to check valves, i.e., valves permitting fluid flow in one direction but blocking flow in the reverse direction.
2. Brief Description of the Prior Art
Check valves have been in existence for many years. They are used where flow is desired in one direction but not in the opposite. For example, check valves are normally installed at the discharge of pumps and compressors, in elevated piping, and in many other applications.
The most common type of check valve is the swing check valve which employs a pivoting flapper or disc which is normally biased by its own weight or a spring to the closed position. Flow in the desired direction swings the disc away from its seat permitting fluid to flow thereby. This type of check valve is noisy, particularly in pulsating flow and at low rates of flow has inherently poor pressure drop characteristics.
There are also check valves which employ ball type closure members. However, in most of these ball check valves, the ball member is always in the path of flow, increasing pressure drop through the valve and preventing passage of tools therethrough. Thus, they are not acceptable for oil and gas wells where it is desired to pass well tools or other equipment through the pipestring. Neither are they desirable in oil and gas pipelines, since it is not possible to pass pipeline pigs through such check valves.